Opis: A nuclear submarine is going through its shakedown cruise. The subs sonar operator picks up a contact dead astern heading straight for them at high speed. The captain orders the vessel to flank speed and sends the sub to battle stations while beginning evasive maneuvers.As the sub dives away from the object, something hits the vessel, and radiation warning sounds throughout the ship. Inspecting the detectors, the crew realizes the source of the radiation is outside the sub. With a jolt the boat comes to a complete stop. The commander immediately orders the sub to surface; this can't be done due to something fouling the diving planes.After a number of unsuccessful attempts, the sub breaks free and manages to reach the surface. During an inspection, the stern of the vessel is found to be radioactive and some sort of organic material, possibly part of a fish, is jammed in one of the control planes.Puzzled, the captain elects to return to Pearl Harbor for repairs and to give a detailed report of the incident. At Pearl Harbor, the sample has been delivered and a team lead by Dr. John Carter (Donald Curtis) and Professor Lesley Joyce (Faith Domerque) begin their investigation, reporting to Commander Peter Mathews (Kenneth Toby).Prof. Joyce is in a very negative mood about the investigation; she fears her own lines of research are going to be affected. Mathew informs her that she has effectively drafted for the investigation and she will be expected to stay involved as long as required and will be compensated for her efforts.Twelve days later, the investigation is ongoing but achieving very little. Mathews has begun to show a definite interest in Joyce. Initially she is cool to Mathews advances, considering him her intellectual inferior. Oddly she is not forthright in telling Mathews to leave her alone. The next day Prof. Joyce makes a breakthrough and discovers what the specimen is. Mathews immediately contacts his superiors and a number of high ranking navy officials are heading to Hawaii to hear the answer.With everyone gathered, Joyce explains the specimen is a piece of a giant octopus. Normally found in very deep areas of the sea, she has a theory that hydrogen bombs have upset its habitat. This caused the beast rise to the surface to find sources of food.It is noted that, in recent times, a number of Japanese fishing vessels have gone missing and the Siberian seal hunting season has failed due to a lack of animals. The naval investigation team is unconvinced by the findings. A few days later a tramp steamer encounters the octopus. The captain orders the crew to abandon ship as the radio operator sends an SOS. In a matter of minutes the ship is engulfed in giant tentacles and dragged under.Unaware of the latest incident, Joyce and Carter attend a farewell dinner with Mathews. As the evening progresses Joyce seems to accept Mathews advances by allowing a long kiss to occur on a quiet balcony. Mathews becomes confused and a little upset when Joyce decides not to change her travel plans.A naval officer interrupts dinner to advise the scientists their travel plans have been canceled. Reports have arrived of the tramp steamer's sinking, and a rescue mission has been launched.Survivors are found and returned to Pearl Harbor. Each man is interviewed and repeats the story of the destruction of the ship. Even after the crew accept lie detectors and interviews by psychologists, the authorities remain unconvinced about the event. Joyce interviews one of the survivors and secretly records the conversation for the navy.On hearing his story first hand, the navy are convinced there is something behind the story; they mobilizes their forces, and close the western Pacific to all ships.A further 10 days pass and Joyce and Carter argue that even if the navy find the creature they have little or no hope of destroying it. To narrow the search, an alert is sent out for any unusual events. The scientists will investigate these events and see if they can narrow down the search area.From Astoria, Oregon, a strange report comes through. Joyce and Mathews investigate a strange set of markings found on a beach and reports of a very strange car accident. They also continue to explore their relationship.It is suggested the beach be closed to avoid any further chance of further attacks. A local sheriff thinks the whole thing is a waste of time and decides to explore the beach for himself. In short order he is killed.The navy sees this as strong evidence of the creature's movement and begin to narrow their search around San Francisco, even deciding to lay a series of minefields around the bay. A trap is set using dead sharks as bait. Aircraft patrol overhead waiting for any sign of the beast. It has been decided the only way to be sure of destroying the creature is to damage the brain. Amid the tension, Joyce reveals a new jet propelled torpedo that might be successfully deployed against the creature.A command center set up by the military reports that an unknown contact is moving towards San Francisco harbor. As planned they begin detonating the mine fields in hope of driving the creature off. The mines have no effect and the second stage of the defense is put into action. An electrical current is run through the Golden Gate bridge and into the water. Enraged, the creature surfaces.Joyce and Mathews rush to the bridge to get a firsthand look at what they are fighting. Carter understands that unless he shuts the power off there is a serious risk to the bridge. To succeed he has to go out onto the deck and expose himself to the outraged octopus.The creature continues attacking the bridge, destroying Carter's car. Mathews sees Carter is trapped and drives out to rescue him. Carter finally shuts the power down and the beast slips beneath the waves.The creature surfaces near the Market Street docks and begins destroying everything in its path. Mathews rejoins his sub with orders to attack the creature. From the shoreline soldiers armed with flame throwers force the creature back into the water. This give Mathews the clear shot he is looking for.The attack is successful but in its thrashing around the creature pins the sub on the bottom of the harbor. Mathews can't detonate the torpedo until the submarine is clear or he risks killing the crew. Mathews dons scuba gear and goes out to attack the creature. Although partially successful he himself is badly wounded and sinks to the bottom. Carter then replicates Mathews efforts, however he aims for the creature's eye. The attack works and the creature convulses from the injury and releases the sub.Carter finds Mathews on the sea floor and races him to the surface before the sub detonates the explosive, obliterating the giant octopus. After the explosion the submarine surfaces to find the two alive and floating on the surface.The trio of Joyce, Mathews, and Carter later celebrate the victory at a restaurant, where Mathews makes an impromptu proposal, and Joyce accepts.